Potassium nitrate

The chemical compound potassium nitrate, a component of saltpeter, or potassium nitrate is a nitrate whose formula is KNO₃. Currently, most potassium nitrate comes from the vast deposits of sodium nitrate. Sodium nitrate is purified and then reacted in a solution with potassium chloride (KCl), in which the less soluble potassium nitrate crystallizes.

Historical production

From mineral sources

In ancient India, saltpeter makers formed the Nuniya caste. Saltpeter is mentioned in Kautilya's Arthashastra (compiled between 300 BCE and 300 CE).), which mentions the use of its poisonous smoke as a weapon of war, although its use for propulsion did not appear until medieval times.

The Syrian chemist and engineer Hasan al-Rammah described a purification process for potassium nitrate in 1270 in his book al-Furusiyya wa al-Manasib al-Harbiyya (Book of Military Horsemanship and War Engines). In this book, al-Rammah describes, firstly, the purification of barud (raw saltpeter ore) by boiling it with a minimum of water and using only the hot solution, and then the use of potassium carbonate (in the form of ash of wood) to remove the calcium and magnesium by precipitating their carbonates from this solution, leaving a solution of purified potassium nitrate, which could then be dried. The terminology used by al-Rammah indicated that the gunpowder he was writing about came from china

Already in 1845, nitrate deposits were being exploited in Chile and California.

From caves

The main natural sources of potassium nitrate were deposits that crystallized from cave walls and accumulations of bat guano in caves. Extraction is done by submerging the guano in water for one day, filtering it, and collecting crystals in filtered water. Traditionally, guano was the source used in Laos for the manufacture of Bang Fai rocket gunpowder.

Saltpetería

Potassium nitrate is produced in a saltpeter. The process consisted of burying the excrement (human or animal) in a field next to the nitrates, watering it, and waiting until leaching allowed the saltpeter to come to the surface of the efflorescence soil. The operators then collected the resulting dust and transported it to concentrate it by boiling in the boiler plant.

In addition to "Montepellusanus" (Montpellier), during the XIII century (and beyond) the only supply of saltpeter in all of Christian Europe (according to De Alchimiain 3 manuscripts by Michael Scot, 1180-1236) was "found in Spain in Aragon on a certain mountain near the sea".

In 1561, Elizabeth I of England, at war with Philip II of Spain, was unable to import saltpeter (of which the Kingdom of England had no production of its own), and had to pay "300 pounds of gold&# 3. 4; to the German captain Gerrard Honrik for the manual "Instructions for making salpeter to growe" (the secret of the "Feuerwerkbuch" - the saltpeter works-).

Salt Bed

Nitrate bedding is a similar process used to produce nitrate from feces. However, unlike the process based on nitrate leaching, the excrement is mixed with the soil and soil microbes are expected to convert the amino-nitrogen into nitrates through nitrification. Nitrates are extracted from the soil with water and then purified in saltpeter by adding wood ash. The process was discovered in the early 15th century century and was widely used until the Chilean deposits were found.

The Confederate side of the American Civil War had a significant shortage of nitrate. Consequently, the Nitre and Mining Office was created to encourage local production, including through nitrate beds and providing excrement to government nitraters. On November 13, 1862, the government placed an advertisement in the Charleston Daily Courier requesting 20 or 30 "fit black men" to work on the new saltpeter beds of Ashley Ferry, S.C. The saltpeter beds were large rectangles of decomposed dung and straw, moistened weekly with urine, "dung water" and liquid from toilets, cesspools and drains, and turned regularly. The National Archives released payroll records that account for more than 29,000 people forced into this type of work in the state of Virginia. The South was so desperate for saltpeter for gunpowder that an Alabama official reportedly placed an ad in the newspaper asking that the contents of the urinals be saved for collection. In South Carolina, in April 1864, the Confederate government forced 31 enslaved people to work at the Ashley Ferry Nitre Works outside Charleston.

French method

Anne Robert Jacques Turgot and Lavoisier created the Régie des Poudres et Salpêtres a few years before the French Revolution. The saltpeter beds were prepared by mixing manure with mortar or wood ashes, common earth and organic materials such as straw to give porosity to a compost pile that used to be 1.2 m high, 1.8 m wide and 4, 6 m long. The pile was usually sheltered from rain, kept wet with urine, turned frequently to speed decomposition, and finally leached with water after about a year, to remove soluble calcium nitrate which was then converted to potassium nitrate by filtration through potash.

Perhaps the most comprehensive analysis of nitrate production is LeConte's 1862 text, which he wrote for the express purpose of increasing production in the Confederate States to meet their needs during the American Civil War. Since he was asking rural farming communities for help, the descriptions and instructions are simple and explicit. He details the "French method," along with several variations, as well as a "Swiss method." N.B. Many references have been made to a method using only straw and urine, but there is no such method in this work.

Swiss method

LeConte describes a process in which only urine is used and not manure, calling it the Swiss method. The urine is collected directly, in a sand pit under a stable. The sand itself is mined and leached for nitrates, which are then converted to potassium nitrate using potash, as above.

From nitric acid

From 1903 until the time of World War I, potassium nitrate for black powder and fertilizers was produced on an industrial scale from nitric acid produced by the Birkeland-Eyde process, which used an electric arc to oxidize nitrogen from the air. During World War I, the newly industrialized Haber process (1913) was combined with the Ostwald process from 1915, enabling Germany to produce nitric acid for warfare after running out of supplies of mineral sodium nitrates from Chili.

Summary

Potassium nitrate is obtained by neutralizing basic compounds (e.g. potassium hydroxide KOH) with nitric acid HNO₃.

The hydrogen atom (H) of HNO₃ joins with the hydrogen (H) and oxygen (O) atoms of KOH, forming water (H₂ EITHER); and the potassium (K) surplus from the KOH with the nitrate (NO₃) surplus from the HNO₃:

KOH + HNO₃ → H₂O + KNO₃

There is also a naturally occurring mineral called nitro, which is usually combined with nitratine (sodium nitrate) to form saltpeter.

Properties

Potassium nitrate has an orthorhombic crystal structure at room temperature, which transforms into a trigonal system at 129 °C.

Potassium nitrate is moderately soluble in water, but its solubility increases with temperature. The aqueous solution is almost neutral, exhibiting pH 6.2 at 14 °C for a 10% solution of commercial powder. It is not very hygroscopic, absorbing approximately 0.03% water at 80% relative humidity for 50 days. It is insoluble in alcohol and is not poisonous; it can react explosively with reducing agents, but it is not explosive by itself.

Uses

As fertilizer

Potassium nitrate is used in fertilizers as a source of nitrogen and potassium, two of the macronutrients of plants. When used alone, it has an NPK index of 13-0-44. Potassium nitrate is the most widely used source of potassium in fertigation, and its consumption is widespread in all types of crops, both annual and permanent. The product when applied does not leave any residue, providing only useful elements, since it is soluble in its entirety. By providing nitrogen in nitric form, not retained by the soil, its distribution is very homogeneous. Its form of application consists of preparing a mother solution, from which it is incorporated into the irrigation water. Approximately 75% of potassium nitrate is manufactured at 90% purity for use as a fertilizer. The absence of chlorine is an advantage for citrus and tobacco plantations, it is also used in the production of liquid fertilizers and is an important constituent of multinutrient fertilizers.

Nitric acid production

One of the most useful applications of potassium nitrate is the production of nitric acid, by adding concentrated sulfuric acid to an aqueous solution of potassium nitrate. It is also an endothermic reaction.

As a food preservative

Potassium nitrate has been a common ingredient added to salted meat since ancient times or the Middle Ages. Widespread adoption of the use of nitrate is more recent and is linked to the development of large-scale meat processing. The use of potassium nitrate has been largely abandoned due to slow and inconsistent results compared to sodium nitrite compounds such as "Prague powder" or the "curing salt" pink. Even so, potassium nitrate is still used in some food applications, such as salami, dry-cured ham, delicatessen, and (in some countries) in the brine used to make corned beef (sometimes together with sodium nitrite).). When used as a food additive in the European Union, https://ec.europa.eu/food/food-feed-portal/screen/food-additives/search/details/POL-FAD-IMPORT-3061 this compound may be designated on the label as E252; it is also approved for use as a food additive in the United States and Australia and New Zealand (where it is listed under INS number 252).

Other uses

25% of potassium nitrate production is technical grade, with a minimum purity of 99%, of which practically 50% is used in metallurgy, mainly in heat transfer baths, between 10 and 20% is consumed by the glass and ceramic industry.

It is also a major component in compounds used to break down organic debris, such as tree stumps, more quickly because it speeds up the decomposition process.

Popular belief is that potassium nitrate is an anaphrodisiac, but it doesn't really have that kind of effect in humans.

Finally, potassium nitrate is the oxidizing agent (oxygen supply). Although potassium nitrate is used to produce gunpowder, mixed with sulfur and charcoal, by itself it is neither combustible nor flammable.

It is also widely used for the treatment of hypersensitivity that affects the dental pulp.